The present invention relates to a matrix clamp for dentistry.
More particularly, it relates to such a matrix clamp which has a threaded rod which is displaceable in a frame in a screw fashion, a coulisse block which is slidingly guided over the frame by the front end of the threaded rod and releasably holds by guiding slots the ends of a width-adjustable loop of a matrix band, and a screw element having an inner thread which engages an outer thread of the rear end of the threaded rod, wherein the rear end of the threaded rod is provided with a knurled handle.
In a matrix clamp of this type which is well known from frequent use, the guiding slot for engaging of the matrix band which is adjustable as to its width to form a loop is arranged at the front end of the frame. The ends of the matrix band are clamped in the front end of the threaded rod and the coulisse block. The coulisse block has a substantially U-shaped cross-section and guided by means of a rivet in a longitudinal hole of the frame. The rear end of the frame is bent in a U-shaped fashion and engaged by the threaded rod in an opening. The free fork-end of the frame engages an outer groove of a knurled nut as a screw element in a form-locking manner. The rear end of the threaded rod is provided with a knurled handle. The clamping and releasing of the free end of the matrix band between the front end of the threaded rod and the coulisse block can be performed by the knurled handle. By means of the knurled nut, the threaded rod and thereby the coulisse block and the free end of the matrix band can move in both longitudinal directions of the frame. The dentist presses down with the finger or thumb of its hand the matrix band applied around the tooth, while with his other hand he has to perform the time consuming screwing work for the matching narrowing of the loop of the matrix band. This screwing work cannot be eliminated even when the thread of the threaded rod formed as fine thread can be replaced with a thread of greater pitch. The reason is that for fine tightening of the matrix band to the configuration of a tooth to be treated, a fine adjustment in form of a fine thread is required.
In a further matrix clamp of this type known as Toffelmire, the coulisse block is composed of a parallelepiped-shaped body with an inclined slot for clamping the ends of the matrix band by the front end of the threaded rod engaging in the slot. In this matrix clamp the coulisse block has a dove-tail guide and is arranged slidingly on a frame rod provided with a corresponding cross-section. The front end of the frame is bent and provided with three different U-shaped guiding slots for guiding the matrix band.
The matrix band before the slots is shaped as a conical loop with an adjustable width and a configuration matching the teeth. In this case the matrix band is not formed as a regular band article, but instead is to be made as an individual item in form of a special band which due to its cutting assumes a conical shape during winding to the loop. In this matrix clamp a guiding slot is provided at both at the end side and at the left and right side of the front frame end. Also this matrix clamp possesses the disadvantage of a time consuming screwing work for narrowing and for expanding the matrix band applied on a tooth to be treated.
The last described matrix clamp possesses the disadvantage in that for resetting the matrix band from the left to the right position, the clamping between the end of the threaded rod and the respective coulisse block has to be released, then the band is reset and the clamping must be again produced. Since here the clamping is released in a positive fashion, therefore during conversion the clamp ends of the matrix band can slide between the clamping parts and must be then again inserted in a time consuming operation. As a result, damages to the matrix band are often unavoidable. The same is true with respect to the insertion and exchange of the matrix band. Further, in both matrix clamps the coulisse block is prescrewed in the front position in which it expands the loop of the matrix band. After placing the matrix band on a tooth to be treated, the respective coulisse block must be screwed back for narrowing the loop of the matrix band in a time consuming screwing operation.
Both above described matrix clamps operate under ergonomically unfavorable conditions in or in the immediate vicinity to the mouth opening of the patient. The reason is that the dentist must hold the matrix clamp with the fingers of one hand and simultaneously press down the matrix band onto the tooth, while with its indicating finger or thumb of another hand he must performing the screwing work for narrowing and expanding the loop of the matrix band.